1. Field of the Invention
The present invention relates to oxide superconducting materials and method for their preparation. It especially relates to a novel copper oxide superconducting material containing carbonate radicals and preparation methods thereof without using an apparatus for storing and supplying CO.sub.2 gas. Furthermore, this invention relates to Josephson junctions using the novel superconducting material.
2. Description of the Prior Art
Several types of copper oxide superconductors have been discovered since high-T.sub.c superconductivity was detected in the La--Ba--Cu--O system. Superconductivity would arise from the layered perovskite-like structure having CuO.sub.6 octahedra, or CuO.sub.5 pyramids, or CuO.sub.2 square planes as a building unit. The layered perovskite-like structure and a sufficient carrier concentration of the material are essential factors for making the material superconducting as indicated by Osamura & Zhang (Japan.J.Appl.Phys.26, L2094-L2096, 1987). In this reference, a series of samples with nominal composition Ba.sub.8 YCu.sub.4 O.sub.16-d did not show any superconducting properties. It is considered that these samples have not sufficient hole concentrations to generate such properties.
On the other hand, a compound Sr.sub.2 CuO.sub.2 CO.sub.3 having CO.sub.3 anions is known to contain layers of CuO.sub.6 octahedra (Hirai et al., Nikkei Chyodendo 6-7, Feb. 3, 1992), but this compound was not made superconducting. The presence of carbonate as an impurity is known to degrade superconducting properties. Therefore, in the preparation of copper oxide superconductors much effort has been given to eliminate the carbonate impurity, and thus nobody is convinced of a superconducting material in which carbonate radicals are incorporated in the structure.